The invention relates to a fluid power apparatus, in particular a marine steering apparatus particularly for use when a conventional, manually-operated helm pump to effect steering of a rudder of a marine vessel.
Helm pumps are well known for actuating rudders of marine valves, a typical helm pump being found in U.S. Pat. No. 3,935,796 issued to Teleflex Inc., inventor Robert A. R. Wood. In this patent, swash plate pump is manually rotated to supply fluid under pressure to one portion of the rudder actuator, and to receive fluid from the opposite portion of the rudder actuator. The patent discloses a variable delivery pump so that, in relatively calm seas where rudder forces are relatively low, the pump is operated in a relatively high flow delivery configuration, such that relatively few turns of the helm delivers sufficient fluid to actuate the rudder from lock to lock. In heavier seas which impose higher force on the rudder, the flow delivery of the pump can be manually changed to a relatively low flow delivery configuration, and many turns of the helm are then required to actuate the rudder from lock-to-lock. This reduces forces on the helm, and operator fatigue.
To overcome operator fatigue for larger vessels, it is well known to provide a power steering system in which an engine driven pressurized fluid supply is directed through a directional valve to an appropriate side of the rudder actuator, to move the rudder in the desired direction. The directional valve is actuated by the helm, and when the pressurized fluid supply is available, a relatively small number of turns of the helm is required to shift the rudder from lock to lock, with relatively little operator fatigue. However, should the pressurized fluid supply fail, a manually operated emergency steering system is required, and this is usually a direct mechanical system which usually requires direct manual engagement and some considerable operator force which cannot be sustained for long periods.
It is known to provide a power steering system as above described with a hydraulically actuated helm pump back-up system which is available should the pressurized fluid supply fail. In one example known to the inventor, as supplied by Hynautic Inc. of Florida, U.S.A., should normal pressurized fluid supply fail, a manually actuated helm pump is available to permit shifting of the rudder with a helm force less than that would be encountered with the normal direct mechanical emergency steering system. However, the Hynautic system known to the inventor involves many components which require separate installation in the vessel, with extensive hydraulic plumbing connections and adjustments, which increases the cost of installation and servicing of the system.